A large number and variety of applications have found value in measuring static and dynamic torque as applied to a rotating shaft. Common static torque is thought to be a steady-state torque having no acceleration component, whereas dynamic torque includes acceleration. Torque is typically measured with one of two methods: inline and reaction. To measure torque inline, sensors are attached into the line of torque transmission, for example, between a motor and the shaft driven by the motor. For reaction torque measurements, sensors derive a value of torque applied to a driven shaft by measuring the torsion, deformation, or strain on the driven shaft. Today, reaction torque sensors are most commonly strain gauges, where foil-based resistance materials are fastened to the exterior of the shaft and strain is measured as forces are applied to the foil material. These sensors require power, often supplied through rotational transformers and a means to read sensor values, commonly by the use of slip rings.
The rotational transformers, associated electronics, and slip rings can make these reaction torque sensors costly and prone to reliability and maintenance issues. Other reaction torque sensors are precise and have the advantage of non-contact sensing. However, such reaction torque sensors may require the attachment of piezoelectric quartz-based surfaces to the rotating shaft and the use of complex electronics, and can be costly to manufacture. Inductive and magnetic approaches to measuring reaction torque have not yet successfully competed against the strain gauge and SAW (surface acoustic wave) sensors. Other approaches, using accelerometers and larger strain gauges that support motors and other power train components, are also in use. Many of these approaches are complex, physically and/or electromagnetically fragile, require many sensor units, and may be costly to fabricate.